content-visibility

<content-visibility> is a simple web component encapsulates modern CSS properties content-visibility and Web API Intersection Observer API to provide cross-browsers solution to skip rendering (layout & painting) elements until it is needed (appears on the viewport) to boosts page performance.

CSS content-visibility is only supported on Chrome 85+, Chrome Android 85+ and Opera 71+ but not Firefox, Safari and IE unfortunately, see web.dev. Intersection Observer API supports pretty much all browsers except IE, thus an intersection observer polyfill is included for compatible on IE.

Basically, all children inside it will only be renderred after it appears on viewport.

<content-visibility>
  {children will not be rendered when outside the first viewport}
</content-visibility>

Compatibility

Getting started

Install

npm i content-visibility --save

Use in JSX (React/Preact)

import 'content-visibility';

const Content = () => {
  return (
    <content-visibility>
      <Section>...</Section>
      <Section>...</Section>
      <Section>...</Section>
    </content-visibility>
  );
};

properties

containIntrinsicSize

This is will be set as CSS custom variable for contain-intrinsic-size if browsers support it. see

<content-visibility containIntrinsicSize="600px">
  {children}
</content-visibility>

Performance results

Rendering frames

Safari comes with Rendering Frames Timeline tool helps to measure rendering performance. Let's have a look the rendering frames without <content-visibility>, total 97 rendering frames happened on the first view.

Only 47 rendering frames happened on the first view after integrated with <content-visibility> the rest of 50 rendering frames happened when scorlling to the viewport

Rendering & Layout time

Generally speaking, we can plausibly say rendering & layout time improved around 40%, however benchmark results vary depends on sampling size, environments, tools, implementation and etc. Too many factors could impact benchmark results, so this is just a quick sample results to demonstrate the performance differences.

Chrome 87.0.4280.141

CSS content-visibility and contain-intrinsic-size

Before

After

Rendering and Painting time reduced around 50%.

Firefox 84.0.2

Before

After

License

Copyright (c) 2021 Brian YP Liu